This invention relates generally to absorbent structures used in disposable articles such as diapers, children's training pants, feminine care articles, incontinence articles, bandages, and the like, and more particularly to such absorbent structures having enhanced liquid intake performance characteristics and to the evaluation and characterization of the liquid intake performance of such absorbent structures.
Conventional disposable articles typically include an absorbent structure, also sometimes referred to as an absorbent core or absorbent composite, formed by air-forming, air-laying or other known forming technique. For example, the manufacture of such an absorbent structure may begin by fiberizing a fibrous sheet of hydrophilic material in a fiberizer or other shredding or comminuting device to form discrete fibers. In addition, particles or fibers of superabsorbent material, which are water insoluble, water swellable and capable of absorbing up to at least about ten times their weight in 0.9 weight percent sodium chloride solution in water (saline solution), are mixed with the discrete fibers. The hydrophilic fibers and superabsorbent material are then entrained in an air stream and directed to a foraminous forming surface upon which the fibers and superabsorbent material are deposited and accumulated to form the absorbent structure.
There is a continuing effort by absorbent structure manufacturers to improve the liquid intake performance of absorbent structures to thereby reduce the tendency of such a structure to leak as it becomes increasingly saturated during use, particularly where the structure is subjected to repeated liquid insults before being discarded. For example, one means of reducing the leakage of absorbent structures has been the extensive use of superabsorbent materials. Recent trends in commercial absorbent structure design have generally been focused on using a higher concentration of superabsorbent material and less fiber in an effort to make the absorbent structure thinner and more dense.
However, notwithstanding the increase in total absorbent capacity obtained by increasing the concentration of superabsorbent material, such absorbent structures may still leak during use. The leakage may be in part the result of the structure having an insufficient intake rate, e.g., the rate at which a liquid insult can be taken into and entrained within the structure for subsequent absorption by the superabsorbent material. More particularly, the intake rate of such absorbent structures may decrease upon repeated insults thereof due to the tendency of the superabsorbent material within the structure to swell as it absorbs and thus restrict or otherwise block the open channels between superabsorbent particles, or between the particles and the hydrophilic fibers within the absorbent structure. This phenomenon is often referred to as a form of gel-blocking and may occur as a result of the superabsorbent material lacking sufficient gel integrity or reaching such a high degree of swelling that it tends to be easily deformable under an external pressure, such as those loads applied by a wearer during movement or upon sitting down. The deformation under load causes the superabsorbent particles to block the open channels within the absorbent structure.
The intake rate of an absorbent structure upon repeated insults thereof is thus considered to be a key parameter for evaluating the in-use liquid intake performance of a disposable article incorporating such an absorbent structure. To date, research into improving the intake rate of absorbent structures has generally focused on the permeability of the absorbent structure, with the general belief that increasing the absorbent structure permeability will lead to increased liquid intake rates. However, the relationship between absorbent structure permeability and the intake rate of an absorbent structure upon repeated insults thereof may be informal at best and absorbent structure permeability, by itself, may be a sometimes inaccurate or otherwise inconsistent evaluating tool or predictor of the intake rate of an absorbent structure. This may be due to the fact that absorbent structure permeability is typically measured with the absorbent structure in a fully saturated state—a condition which rarely occurs for absorbent structures in actual use.
There is a need, therefore, for absorbent structures having enhanced intake performance characteristics, and for a more reliable means of evaluating and predicting the intake performance characteristics of absorbent structures, and more particularly for evaluating and predicting the intake rate of such absorbent structures upon repeated insults thereof.